Abstract: In order to make full use of the resources in Magnolia kwangsiensis Figlar & Noot. (M. kwangsiensis), the stability and antioxidant activity of polyphenols from M. kwangsiensis leaves were studied. Taking the crude extracts and the purification of polyphenols from M. kwangsiensis leaves as the research object, the effect of the different light, temperature, sugar, preservative, oxidant and reductant on the stability of polyphenols was investigated, and the antioxidant activity of polyphenols was evaluated in terms of·NO scavenging activity and·OH scavenging activity. The retention rates of polyphenols crude extracts and purification from M. kwangsiensis leaves were 53.75%, 57.50% under the dark for 1 h, and were 54.30%, 81.58% under the dark, at 30℃ for 1 h, respectively. The preservative sodium benzoate had a positive effect on the stability of polyphenols, and the retention rate was positively correlated with the sodium benzoate concentration. The oxidant hydrogen peroxide and reductant sodium sulfite had negative effect on the polyphenols from M. kwangsiensis leaves, and the effect of oxidant was stronger than of reductant. In the range of 0.01~0.05 μg/L concentration, polyphenols crude extracts and purification from M. kwangsiensis leaves had some scavenging effect on the·NO and·OH radical with dose-effect relationship. This article would have great importance to promotintroduction breeding, develop new natural product and the natural food additive.